no sound on external calls

I have used both 3cx phone (for iphone) grondwire (for iphone) and telephone (for OSX) and none of these have been able to get audio on any call out side of my office. my server has no firewall and is in a DMZ (all ports open) on my router. i get calls fine in the office. but as soon as i leave the wifi of my office my calls have no audio. i can dial and the phone or extention i call will ring but there is no voice from either person. If i record the call i can hear the other person on the play back but not my self.

i have the voip client set to the proper dynamic dns settings. and like i said i can make and receive calls so the client is working at least on 5060. also i noticed that when i use groundwire is shows what codec i am useing, at the office i use "μ-law" but when i leave the office it uses ?/μ-law which make me think that the server codec is not corect.

It sounds like the "no audio' issues are happening while on "other" Wifi networks, correct? And i assume that this is a 3CX extension?

Be sure that the phone is set to use STUN when outside the local LAN. Check the 3CX logs for when the phone registers from a remote LAN. Do you see a private IP registering or a public IP, It should be a public IP or you will get the lack of audio issues.